Romantic comedies are a little like junk food: they're not healthy or sophisticated but, when made right, there's something addictive about their tasty familiarity. Going in, you know what you're going to get. There are no surprises, nasty or otherwise. The guy will capture the girl's heart (or vice versa) and the courtship rhythms are pre-ordained. The story is so familiar that it's like watching a re-run of something you have seen before but with different actors, a different locale, and (if you're lucky) a few new twists. Romantic comedies are popular because they are non-threatening and offer wish fulfillment. Failed examples typically don't work because the screenplay isn't sufficiently focused on the romance or because the leads are mis-matched. "Chemistry" is an overused term in the film industry, but it is, without question, the #1 factor in determining the effectiveness of a motion picture residing in this genre.

No Strings Attached, Natalie Portman's follow-up to her likely Oscar nominated role in Black Swan, falls into the competent-but-not-terrific category. It does most of the romantic comedy things right, including offering occasional laughs, providing a host of annoying and/or pointless secondary characters, and saving declarations of love for the last act, even though it's clear the feelings exist long before they are voiced. To the extent that there's a problem, it can be laid at the feet of the male lead. While there's nothing about his character that's a stretch for Ashton Kutcher, the actor's limitations are evident from the beginning. He looks good, but these still waters don't run deep. If one was to pick a male lead based primarily on physical appeal, Kutcher might be a good choice, but even in a movie with as thin and threadbare a plot as this one, he brings too little to the production. There are fitful sparks between him and Portman, but he is unable to sustain viewer interest in his character. She becomes the dominant figure and that throws off No Strings Attached's balance and impacts the all-important chemistry.

This would seem to be a paycheck opportunity for Portman and, in the past, such films have not always elicited top-notch performances. Here, perhaps because the role appears to have been tailored to her strengths, she's credible. Emma is smart, emotionally reserved, and not given to emotional outbursts - perfect for Portman, whose least effective moments are often the most emotionally charged ones. She's not in form here (not that anyone would expect her to be), but there's nothing in her portrayal that will negatively impact any awards aspirations. Interestingly, this is her first formulaic romantic comedy (Garden State doesn't count - that had a "quirky, indie" vibe); it's an oddity for a young, attractive actress to have been in the business for 17 years before appearing in one of these.

No Strings Attached fits into the romantic comedy category of sex-partners who violate their "no emotions involved" agreement and fall for each other. They are Adam (Kutcher), a TV series production assistant with aspirations of writing a script, and Emma (Portman), a doctor struggling through her residency. Their paths, which have briefly intersected several times in the past, collide when Adam's girlfriend dumps him for his famous father (Kevin Kline). After getting drunk, he starts calling every number stored in his cell phone and this leads him inevitably to Emma. The next morning, after he has recovered from being passed out in an apartment she shares with three roommates, they have sex and form a pact: each will be available whenever the other wants sex, no strings attached. If emotions become involved, however, they will have to terminate the agreement.

No Strings Attached boasts an interesting supporting cast. The spotlight-stealer is Kevin Kline who, despite being in only a handful of scenes, is the most memorable character in the movie. Other parts are filled by mumblecore queen Greta Gerwig as Emma's pretty roommate, Lake Bell as one of the people to whom Adam is an assistant, Cary Elwes as a staff doctor at the hospital where Emma works, Ludacris as one of Adam's friends, and Olivia Thirlby as Emma's sister. Since no standard romantic comedy comes without romantic complications, Bell fills that function.

Director Ivan Reitman, whose overall resume is impressive but who hasn't made anything memorable in about 20 years (in contrast to his son, Jason, whose Juno and Up in the Air have received recent Oscar consideration), has abandoned the "safe" PG-13 approach and instead opted for the more adult-oriented R. The choice is intentional; the core content may be PG-13 but the more restrictive certification was obtained by adding some gratuitous profanity. It's curious that, at a time when so many films are being sanitized to get a PG-13 rating that Reitman has elected to go in the other direction. He is obviously pitching the movie at twentysomethings not teenagers.

Despite the rating, there's nothing edgy about No Strings Attached. The movie's weaknesses are evident when it is compared to the similar Love and Other Drugs, which addressed the same idea of fuck-buddies developing an attachment with a greater sense of urgency and honesty. Aside from the dubious choice of Kutcher as the male lead, No Strings Attached suffers from snatches of poorly written dialogue. Although there are some genuinely amusing lines in the movie, none are as hilarious as the riper, unintentionally funny ones. At the screening I attended, audience members were laughing a lot, but not always at things Reitman intended.

For the romantic comedy audience - those who attend movies of this genre out of a genuine love for this sort of thing - No Strings Attached delivers what it promises. Others need not bother, but they probably wouldn't have, anyway. The film is pleasant enough, if inconsequential, and will do nothing to help or hurt the careers of those involved. That it's being released when Portman is suddenly hot is a bit of serendipity (the release date was set before she was viewed as an Oscar contender), but that may not provide a tangible boost at the box office. No Strings Attached is what it intends to be, with no pretentions or apologies. Based on personal preferences, each potential viewer will know whether they'll like it or not before attending.